Reliability Centered Maintenance (Rcm) For Asset Management In Electric Power Distribution System'

ABSTRACT

Ability to use electrical energy when required is one of the fundamental presumptions of a modern society, and the introduction of complex and sensitive machines and systems into the network had increased the need for high reliability of supply [1]. Deregulation and competition are forcing improvements in efficiency and reductions in cost while customers are becoming more sensitive to electrical disturbances and are demanding higher levels of service reliability. Since a typical distribution system accounts for 40% of the cost to deliver power and 80% of customer reliability problems, distribution system design, operations and maintenance are critical for financial success and customer satisfaction [2]. Moreover, failure statistics [3] reveal that the electrical distribution systems constitute the greatest risk to the uninterrupted supply of power. Traditionally however, distribution systems have received less attention than the generation and transmission parts of the overall electrical Power systems. This is emphasized by the clear difference in the number of publications within the various relevant fields [4]. The main reasons why distribution systems may not have been the centre of focus are that they are less capital-intensive and that their failures cause more localized effects compared to generation and transmission systems. However the focus on generation and transmission systems is moving toward distribution as the business focus changes from consumers to customers [4]. Electrical power systems have undergone major changes during the last few years due to the introduction of the deregulated or liberalized market. (Sweden, for example, was one of the first countries to deregulate its power- supply market. This happened in January 1996) [5]. This has implied that the driving factors have moved from technical to economical. New players are now making their appearance in the field. This fundamental and global-level change in the running 2 of power utilities has brought about diversity effects, including new opportunities and new complications. These utilities are themselves active in the deregulated market and face various market challenges. For example, customers pay for energy delivered while authorities impose sanctions/regulations, they supervise and they compensate customers depending on the degree of fulfillment of contractual and other obligations as recommended [6,7]. On the other hand, the owners expect the utilities to deliver at minimum cost. This means that electricity utilities must satisfy quantitative reliability requirements, while at the same time try to minimize their costs. One clear and predominant expenditure for a utility is the cost of maintaining system assets, for example through adopting preventive measures, collectively called preventive maintenance (PM). Preventive maintenance measures can impact on reliability by either, (a) improving the condition of an asset, or (b) prolonging the lifetime of an asset [8]. Reliability on the other hand, can be improved by either reducing the frequency or the duration of power supply interruptions. PM activities could impact on the frequency by preventing the actual cause of the failure. Consequently, in cost- effective expenditure, PM should be applied where the reliability benefits outweigh the cost of implementing the PM measures [9]. Traditionally, preventive maintenance approaches usually consist of pre-defined activities carried out at regular intervals (scheduled maintenance). Such a maintenance policy may be quite inefficient; it may be costly (in the long run), and it may not even extend component lifetime as much as possible. In the past several years, therefore, many utilities replaced their maintenance routines based on rigid schedules by more flexible program using periodic or even continuous condition monitoring and data analysis [10]. Research findings have shown that maintenance impacts on the reliability performance of a component, that will eventually reflect on the entire system since power systems is made up of interconnected components[11]. Many programs had been used to validate this 3 fact, such as failure effects analysis, an evaluation of needs and priorities, and flow charts for decision making [12]. Some of these approaches have been collectively termed Reliability-Centred Maintenance (RCM) [13]. In a RCM approach, various alternative maintenance polices are compared and the most cost-effective is selected.